Insulating material and method of producing the same



Jan. 17, 1928.

A. R. KEMP 1,556,737

INSULATING MATERIAL AND METHOD OF PRODUCING TME SAME Filed Feb. 28, 1927 :Sai-Ganas 2'55 6 7 8 S'IO Il I2 I3 I4 I5 I6 I7 I8 I9 20 amy Fianna im. i7, leze.,

y l UNITED STA-ms' PATENT; OFFICE; l

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msm'rmefirnrnann im minion or raonucme 'milj Application led February 28, 1927. Serial, lr'oylllBG. l

`This invention relatesfto insulating :materials, particularly those suitable for insulating conductors of submarine cables, and

Y to methods for producingsuch materials. In accordance with my co ending application, Serial No. 725,691,'le July 12, 1924,

issued on August 9, 1927, as Patent 1,638,535,

there is disclosed a material which is produced by mixing rubber with 8 to 16% sul- 10 phur by weight and heating the mixture '(or the material resulting from vulcanizing the mixture) toa high temperature sufiicient to.

' produce a material having thermoplastic properties similar to those possessed by gutta perche in the temperature'range extending rom temperatures at which gutta percha insulated conductors are ordinarily used to the temperatures employed irie'xtr'uding.`

In accordance with the `present invention there is provided an insulatin material having mechanical properties similar to those of the material of m earlier 'application and somewhat improve electrical properties with respect to its use as submarine cable insulation. Thesu eriority 'of this material results from its ing a mixture in proper proportions of a plurality `of rubber compounds of different c aracteristics. In a referred embodiment ofthe invention, one o the compounds is made 4by mixing approximately 5% sulphur by weight with 95% raw rubber and heated to hi h temperature, preferably about 235 C. an anotherl of the compounds is made in a similar manner from a mixture of 20% sulphur and 80% rubber by wei ht.

The invention may be better understoo by referring to the following description togetherv with the accompanying drawing in which: l

Fig. 1 is a curve showin' the conductance of thermoplastic compoun s the constituents of which comprise raw rubber and sulphur in different proportions, respectively, and

Fig. 2 is a curve showing the dielectric constants of the thermo lastic compounds for which values of conductance areaindicated in the curve of Fig. 1. i

The samples employed in obtaining the curves of Figs. 1 and 2 were prepared b mixing raw 'rubber and sulphur in a stan ard rubber mill. After being thorou hly mixed, the ingredientsy were raised rom room. tem erature to a` temperature of approximate y 225 C. over a period ofl approximately 70'miiiutes and were maintained c at this ltemperature for about 2O minutes.

Heating the mixture to this temperature, which is higher than that required for vul -canizatiom causes a change in the structure of therubber which-is accompanied by the liberation of hydrogen sulphide and which results in changing the material froma substantially non-plastic to a thermoplastic condition. The degree to which the material is I' rendered thermoplastic` depends o n its ,coniposition, the heati'nglltemperaturef and the time forwhich it is subject to heating.. The

samples of thermo lastic material were tested at approximate y room temperature and -tlie dielectric constant was measured at a It has` been found that whenapproximatei 84% to 92% mw rubber by' wei hais i -mixe with from 8 to 16% sulphur an then heat treated as described above, there is produced a material having approximately tlie thermoplastic properties of gutta percha and one whichY is, vtherefore lis-soft and can be extrudedabout a conductor p particularly suited from a mechanical standpoint forinsulating 804 similarly to' gutta perche 4at tem eratures such as are ordinarily maintain during the extrusion process, that is, temperatures,

not appreciably in excess of C. At

room temperature the material becomes' tough and retains its form as is the case with gutta percha. Like 'gutta percha, moreover, the material may be cooled below 0 C. without becoming brittle, i v

As indicated by ythe curves 4ii, material,

l which before vulcanization contains Vapk roxi mately.l121/2% sulphur, has a peak yva ue of conductance, that is,` such a material has a `higher conductance "than fa material' which containsmore or-'less .sulphurv than this amount. Moreover, a material which before vulcanization contained Iapproximately 10% s'ulphur'lias a peak value for itsdielectric constant. An insulating material for submarine conductors should, of course, possess low conductivity and a low dielectric consta-nt' in orderthat-tlie transmission losses caused by the insulation may be suitably ever, that' a. material having the mechanical properties bestjsuited for .anY insulating material Vfor submarine cables, that is, one

which`r before. vulcanization had a sulphur aantehtfoff-eiipresiriiatsly i12 to 14%., has

comparatively poor electrical propcrties. p w

' 86% raw rubber and 14% Vsulpliui-.` It has The curvesf also indicate that a material made of approximately sulphur and95% rubber by .weight, und amaterial made of approximately 20% sulphur and 80% rubber,

possess improved electricaliproperties. '.llhese materials, however', are not suited for. insulatingsubmariiiey `conductors since the one with-the low sulphur contentbefore vulcanization isk toosoft at a. temperature of approximately 0 C. and the` other material is too brittle' at this temperature. p

" Inaccordance withthe present invention A,an insi1'latirig material having mechanical andjjelectrical@properties which make it suitableasyzfan insulating material for submai'iiieconductors is?` pi'oduced'by preparing two'ffinixtures' ofsulphur and raw rubu beii,"" 6nd,`L conipris'ing approximately 95% rubfb'erfi'ajiid 5%;fsulphurxbyfweight and the other comprisingapproximately 80% rubbei;` aridf %"sulphuin After thoroughly l.mixingas..by working on the rolls of a :se

standard.'Jrubberiinill, each mixture is `heated to a temperaturelsiiiiiciently high to produce ffr approximately '235 C'. maintained for a -45mprcessfmay pe continuous, i. e., the tem- 4vulanization, a `temperature of approxi matelyflOO C. maintained for-a period of ap. `'roii'imately 16 hours havin been found lsuitableforthispurpose.: T e nextste in ithe, process is to render the materia ,suitably thermoplastic thisv maybe accomplxished` by. maintaining" the material at a Vtemieratu re well labove. that required to ufce" vulcaniz`ation a: temperature of period` ofjabout r1,0,ho'urs having been found to `v`give satisfactory results. ,Instead of at a low temperature Vthe peraturemay befraised to the high value Without interruption'. The preferred values of,"heating.periods anclftempei'atures for 'producingyulcanization and `for rendering the materialsY suitably thermoplastic n are given above, but somewhat, different f values 'may employed for producing approxilmatel'ythesaine resiilts."fFor instance, ltem- 4peraturesbetween 200:a`nd 280 C. may be employedfor renderin then material suitably vthermoplastic.' he two compounds produced from -the mixtures ofrubber and sulphur arethoroughly fmixed as by work- ,on the rolls of a standard rubber mill eit er before-or after being subjected tothis temperature. ,While these materials maybe mixed various proportions it` has been' found` preferable` to `mix approxi- A mately threerparts kof 'the material which before vulcanizatior'i contained 20% ySillbeen found, moreover2 that mixing together the two thermoplastic materials (or' two vulcanized materials which are heated to a high temperature after mixing) does not appreciably alter their electrical properties, so that the electrical properties, such as dielectric constant and conductivity, of the mixture of the two thermoplastic materials described above are of the same order as those of the tliermoplasticmaterial produced from 95% raw rubber land 5% sulphur or from 80% rubber and 20% sulphur. Y I

The mixture of the two thermoplastic materials is 'now suitable for usein the cxtrusion process for applying insulation to cable conductors. In this process the matei'ial is maintained at a temperature of approximately to 100 C. If desired, however, other materials such as balata or mineral rubber may be mixed with these thermoplastic. materials. Good results have been obtained by insulating submarineiconduc'tors with a material containing the fol lowing ingredients, the percentage of each material being given with respect to the total weight.

Per cent. Plastic material (20% sulphur, 80%

rubber) 38.5 Plastic material (5% sulphur 95% rubber) H. 24. 0 Mineral rubber "14.5 Balata...`. 23.0

In this mixture, the mineral rubber softens the material and thebalatawsome what improves its plastic properties.

The term thermoplastic, as usedin this specification and the appended claims, should be taken to denote tlie'property, possessed by a material, of varying its plasticity in accordance with `variations in its temperature. By qualifying"u "the term thermoplastic in this specification and lli() the appended claims by comparingsuch property with the thermoplastic properties of gutta ercha it is intended that the term, as quali ed, should approximately represent such variations in plasticity as are `manifested by gutta percha within the temperatures, wliich, on one hand, exist at the sea bottom or other places where conductors insulated with gutta percha are ordinarily placed for operation and may be below zero degrees centigiade, and which, onthe other hand, are ordinarily maintained during the extruding process in the manufacture of gutta percha insulated cables and do not exceed 100 C.

What is claimed is:

1. The process of producing an insulating material, which comprises subjecting each of a plurality of compounds the constituents of which comprise rubber and sulphur in different proportions, respectively, to a temperature Well above that required to produce vulcanization, and mixing said compounds.

2. The process of producing an insulating material, which comprises subjecting each of a. plurality of compounds the constituents of which comprise rubber and sulphur in different proportions, respectively, to a temperature between 200 C. and '280 C., and mixing said compounds.

3. The process of producing an insulating material, which comprises preparing two mixturesvo rubber and sulphur in different proportions, respectively, subjecting said mixtures separately to a temperature above that required to produce vulcanization for producing compounds having suitable thermoplastic properties, and then mixing said compounds. j

4. The process of producing an insulating material, which comprises preparing two mixtures of rubber and sulphur in diferent proportions respectively, subjecting said mixtures separately to a temperature between 200 C. and 280G C., for producing compounds having suitable thermoplastic properties, and then mixing said compounds.

5. The process of producing an insulating material, which comprises preparing two mixtures of rubber and sulphur in different proportions, respectively, heating said mixtures at approximatel 150 C. for a period ot' about 16 hours, an heating the resulting compounds, at approximately 235 C. for a period of about 10 hours for rendering the compounds suitably thermoplastic.

6. An insulating material comprising a mixture of a plurality of compounds, the constituents of which comprise rubber and sulphur in different proportions, respectively, which compounds havey been heated to a temperature well above that required to produce vulcanization.

7. Au insulating material `comprising a mixture of a plurality of compounds the constituents of which comprise rubber and sulphur, the constituents of one of said compounds comprising less than 10% sulphur by weight of 'the totl rubber sulphur content and the constituents of the other of the compounds comprising more than 12%75 sulphur by weight of the total rubber sulphur content, 'which compounds have been heated to a temperature Well above that required to produce vulcanization.

of the compound, the constituents of which comprise about 5% sulphur and 95% rubber by Weight.

10. An insulating material comprising a mixture of a plurality of compounds, thc constituents of which comprise rubber and sulphur in different proportions, respectively, whicli compounds have 'been heated to a temperature Well above that required to 'produce vulcanization, and a materials'uch as balata added to the mixture of said compounds. p

In witness whereof, I hereunto subscribe my name this 24th day-of February, A. D.

Aucune n. KEMP. 

